Sealed gas-tight containers require venting when gas pressure must be equalized between the interior and exterior of the container. Without venting, a flexible gas-tight container will bloat, leak, and possibly burst when the interior pressure exceeds the exterior pressure. Bloating can occur when the contents of the container generates gasses or heat by chemical reaction, for example when the contents include a peroxide-based toothpaste. Bloating can also occur when the container is stored in a heated environment. An unvented flexible gas-tight container will collapse when the internal pressure is reduced, for example when atmospheric oxygen is scavenged by one of the ingredients housed in the container. Some modes of transportation put a container at risk of both bursting and collapse. During vehicular transport through mountains and valleys, for example, a container is subjected to pressures that can rise above and drop below sea level pressure. Rigid gas-tight containers, such as glass containers, are susceptible to bursting or imploding if the internal and external pressures become sufficiently discrepant.
One way to equalize pressure is to provide a filter vent in the cap, lid, or other closure of a container. Filter vents generally include a gas permeable filter, or other gas permeable microporous medium, which is interposed between the interior of the container and a vent aperture. The filter vent permits gases to diffuse in and out of the interior of the container, via the vent aperture, while excluding particulates larger than a threshold size, as well as liquids of a particular range of hydrophobicity. The term “filter cap” will be used as a generic term for all container closures fitted with a filter vent.
Filter caps such have a serious drawback. The pores of the filter are susceptible to being filled and clogged by the contents of the container. Existing solutions to this problem are not satisfactory. PCT Application No. WO 97/02994 to Vakharia (“Vakharia”) discloses a gas permeable membrane mounted at an angle to the inner upper surface of a bottle cap. Angling of the membrane is intended to cause liquid to roll off the membrane surface instead of remaining fixed to the membrane surface. U.S. Pat. No. 6,196,409 to Lake et al. (“Lake”) discloses a cap or container including a filter vent that has no structural adaptation to prevent the filter from contacting the contents of the container. Instead, Lake relies on the matching of the filter material to the physicochemical properties of the contents of the container, so that the filter material encourages the phase separation and run-off of contents that have contacted the filter. This material-matching requirement limits the selection of filter materials that can be used with any particular type of contents. Furthermore the encouragement of drainage of container contents after they have contacted a filter is less desirable than the prevention of contact between the contents and the filter in the first place.
Container-mouth baffles, such as sifters, are used to regulate the dispensing of granular materials through the mouth of a container. A typical example is the sifter top disclosed by U.S. Pat. No. 5,513,781, to Ullrich, et al. (“Ullrich”). The sifter top includes a perforated liner extending across the mouth of a bottle suitable for containing spices or similar materials. Sifters typically include perforations large enough to permit the passage of granular materials out of a container.
Container-mouth baffles can potentially protect the filter of a filter cap from the contacting the contents of a container, but they have never been situated, or provided with appropriate perforations, to perform such a protective function. There is a need for assemblies and methods for protecting a filter cap with a container-mouth baffle.